If you name your plane in its name field.....lets say....bomber
_bomb = "maverick" createVehicle setPos [getPos bomber select 0, getPos bomber select 1, (getPos bomber select 2) -2]
This will create _bomb at the position of the plane, but 2 metres below it.
You don't want to create it at the same height as the plane, as it might destroy the plane instead.
At least I hope that will work.....try it.
Planck